There are numerous systems for indicating the presence of mail in a mailbox described in the prior art. For example, see U.S. Pat. No. 4,651,135 which discloses a mail detector for indicating the presence of mail in a mailbox to a postal customer. The mail detector is disposed in the mailbox and includes an indicator on the mailbox and a duplicate indicator in the postal customer's residence to indicate the presence of mail in the mailbox to the postal customer. U.S. Pat. No. 4,520,350 discloses a detector system which includes a wireless transmitter and wireless receiver. When mail is detected by the system, the transmitter sends a signal to the receiver triggering an indicator indicating the presence of mail to the postal customer.
In both of these patents, the described devices are intended to relieve the postal customer of the burdens of checking whether the mailbox contains mail. However, the above described systems do not provide mechanisms to relieve some burdens on the postal carrier. For example, in the event that a carrier has no mail to deliver to a particular postal customer having such a device, the carrier may still have to make a stop at the postal customer's mailbox to determine whether the customer has left mail for pickup by the carrier. In some situations, it may be desirable to indicate the presence of mail to the postal carrier and also the withdrawal of certain mail by the postal customer to the postal carrier or post office. Neither of these devices provide an indication for the postal carrier that the postal customer has deposited mail in the mailbox nor that the postal customer or postal carrier has withdrawn certain mail deposited in the box.